Network Working Group B. Fenner
Internet-Draft AT&T Labs -- Research
Expires: April 24, 2006 M. Duerst
World Wide Web Consortium
October 21, 2005
Formats for IPv6 Scope Zone Identifiers in Literal Address Formatsdraft-fenner-literal-zone-02
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Abstract
This document specifies the format to be used when specifying a zone
identifier with a literal IPv6 address in URIs and IRIs, and in SMTP
and Internet Mail Messages. While this combination is expected to be
needed rarely, it is useful to specify the exact syntax.
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Internet-Draft IPv6 Scope Zones in Literal Addrs October 20051. IntroductionRFC 3986 [RFC3986] defines the IPv6address production for the rare
case that a literal IPv6 address is required in a URI. IRIs
[RFC3987] copy this syntax. The IPv6 Scoping Architecture [RFC4007]
describes the syntax for specifying a zone ID to disambiguate an
ambiguous scoped address. Unfortunately, the IPv6address production
does not permit the format including the zone ID, so this document
defines a method to specify a zone ID with a literal IPv6 address in
URIs and IRIs.
The Simple Mail Transfer Protocol [RFC2821]'s IPv6-address-literal
production provides the same ability for SMTP, so this document
defines a similar syntax to specify a zone ID with a literal IPv6
address for SMTP.
While part of the reason for the deprecation of Site-Local scoped
addresses [RFC3879] was due to applications needing to know about
scope zones, the formats described in this document do not have the
problem described in section 2.1 of that document - specifically,
they always contain the zone ID, so are never ambiguous.
2. Format in URIs and IRIs
The IPvFuture production in URIs and IRIs was created to allow for
flexibility in defining new IP address formats. We use this
flexibility in this format, to add a previously unanticipated address
format for IPv6. Therefore, strings matching this grammar also match
the IPvFuture production in URIs and IRIs. While the form specified
in the IPv6 Scoping Architecture [RFC4007] uses a percent ("%") to
separate the zone ID from the address, this form separates the zone
ID from the address using an plus sign ("+"), to avoid the special
meaning of the percent ("%") in URIs.
; An address matching IPv6scoped-literal also matches
; the URI/IRI spec's IP-literal with IPvFuture
IPv6scoped-literal = "[v1." IPv6scoped-address "]"
IPv6scoped-address = IPv6address "+" IPv6zone-id
IPv6zone-id = 1*( unreserved / sub-delims / ":" )
3. Format in SMTP
Although it usage is expected to be even more rare, there may be a
reason to use a zone ID in an IPv6 literal address in SMTP. An
addition to the ABNF grammar used in the Simple Mail Transfer
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Internet-Draft IPv6 Scope Zones in Literal Addrs October 2005
Protocol [RFC2821] follows.
; An address matching IPv6-address-scoped-literal
; also matches RFC 2821's General-address-literal production
IPv6-address-scoped-literal: "IPv6z:" IPv6-addr "+" 1*dcontent
(Note: while it's possible to use "%" in the SMTP case, we use "+" in
order to align the SMTP and URI syntaxes.)
4. Limitations
The usefulness of a URI or IRI using a literal scoped address is
obviously limited to systems within the same scope. The addition of
the zone identifier further limits the usefulness to the system for
which the URI or IRI was generated, since zone IDs are completely
local to a given host. Therefore, care must be taken to not pass
these URIs blindly between systems. When both systems are aware of
the relevant Zone IDs, e.g., an SNMP manager that is aware of the
zone ID configuration of an agent, it is acceptable to pass these
URIs between systems.
Caution should be used when storing these URIs or IRIs in files. It
is recommended to use an FQDN instead of a literal IPv6 address in a
URL, whenever an FQDN is available.
5. IANA Considerations
IANA is requested to assign the "IPv6z" tag identifying a domain
literal. This registry may not have been created yet; it is
described in [RFC2821] but this will be the first assignment.
This is also the first use of the IPvFuture extension mechanism
described in [RFC3986]; that RFC did not create a registry for these
mechanisms. Should there be one?
6. Security ConsiderationsRFC 3986 [RFC3986] describes security considerations for URIs; this
specification does not add any new security considerations.
7. Acknowledgements
Margaret Wasserman first pointed out that the original literal IPv6
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Internet-Draft IPv6 Scope Zones in Literal Addrs October 2005
o Check with w3c URI
o Check with [who did Brian suggest in Paris?]
o Check with apps area
Appendix B. Change LogB.1. Changes from -01 to -02
Changed "v6" to "v1", since the version number is of the literal
form, not of the address.
Changed "_" to "+", since an underscore disappears when underlined
as URLs are wont to be.
Added section on SMTP IPv6z:
Removed list of tradeoffs.
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Internet-Draft IPv6 Scope Zones in Literal Addrs October 2005
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